Lithium ion storage batteries are used these days so as to achieve high energy densities. As high energy storage batteries, these have energy densities up to about 200 Ah/kg. As high power storage batteries, energy densities up to about 100 Ah/kg are achieved.
The energy density of lithium ion storage batteries used today is not sufficient, however, especially for applications in electric and hybrid vehicles. Using today's technology that is based on intercalation cathodes and intercalation anodes, also only a slow increase in energy density is made possible. This may be attributed to the fact that the intercalation cathodes supply only one-half of the energy density of the anode. For this reason, new concepts are being sought that permit an increase in the energy density of lithium ion storage batteries.
T. Ogasawara et al., “Rechargeable Li2O2 Electrode for Lithium Batteries”, J. Am. Chem. Soc., 2006, 128, pages 1390 to 1393, describes a porous electrode on which lithium reacts directly with oxygen from the air. Using such an oxygen cathode, one is able to achieve 5 to 10 times as high an energy density as with the usual lithium ion storage batteries, which use an intercalation cathode. In order to be able to absorb oxygen and to release it again, it is necessary, however, for the electrochemical cell to be open. On the other hand, however, it must be prevented that water or carbon dioxide from the air get into the cell, since these compounds may lead to side reactions there, which may decisively reduce the power output and the service life or may make the lithium anode unusable. In addition, such side reactions may proceed explosively. In order to prevent water or carbon dioxide from getting to the anode, conventionally, for example, one may use a ceramic diaphragm which prevents moisture or foreign gases from getting to the anode. Using such a diaphragm does not, however, exclude the reaction of the electrolyte with water, and in addition, the mechanical stability of the diaphragm could be a problem. Thus, for example, hydrofluoric acid is formed in the electrolyte by the reaction of LiPF6 with water, which leads to various ageing mechanisms by attacking electrodes, for example.